The invention relates to a latent heat body with paraffin-based latent heat storage material accommodated in a carrier material which has capillary-like holding spaces, the carrier material comprising an organic plastics material or natural material.
From German Utility Model 84 08 966, there is known a porous foam material as the carrier material. However, with this foam material it is impossible to achieve the structural strength desired even when the latent heat storage material is in the heated state. Moreover, the porous foam material cannot readily be impregnated with the latent heat storage material. Special measures, such as squeezing, have to be taken.
working on this basis, the invention deals with the technical problem of providing a latent heat body which, while being easy to produce, is highly efficient, i.e. has a high heat storage capacity and, at the same time, exhibits sufficient structural strength even in the heated state. It is also desired for the carrier material to be filled with or suck up the latent heat storage material automatically, as far as possible. It is also important to achieve a high retention capacity with regard to the latent heat storage material by means of the properties of the carrier material alone.
These technical problems are initially and substantially solved by assembling the carrier material from individual carrier-material elements which are inherently structurally strong or, when combined with the latent heat storage material, lead to the appropriate structural strength, for example by adhesive bonding. For the invention, it is important for the carrier-material elements to be held cohesively together even in the absence of latent heat storage material, and consequently the carrier material is one or more structures each comprising a multiplicity of combined carrier-material elements. According to the invention, the carrier-material elements are assembled in such a way that capillary holding spaces for the latent heat storage material are formed between them, which spaces may be in the form of a crack. The capillary holding spaces described above, due to their capillary action on a fluid, allow the carrier material to be filled with or to suck up the fluid in a substantially automatic manner and provide the carrier material with a high retention capacity. This action is used to good effect for the latent heat body according to the invention in that the proposed paraffin-based latent heat storage material to which individual additives, or a plurality of the additives, cited in this application may be added, is liquefied by heating to a sufficient extent for the automatic suction action to be observed. Preferably, the latent heat storage material can be heated up to a temperature which is above the highest melting point of the individual paraffins and additives contained therein. The latent heat storage material is in this way liquefied to such an extent that it can be taken up automatically by the carrier material until the latter is completely saturated. This procedure results in the advantage that it is possible to dispense with complex and therefore expensive technological process steps which involve a high input of in particular mechanical energy.
The assembly procedure which leads to a fixed bond between the carrier-material elements is at the same time suitable for setting the size of the holding spaces which remain between the carrier-material elements and for influencing the desired structural strength.
By virtue of the adjustability of the size of the holding spaces, there exists furthermore the possibility of establishing, as a function of the boundary or surface tension of the latent heat storage material, a size of the holding spaces which is optimized with regard to a maximum possible holding capacity and, at the same time, a sufficiently high capillary action.
Suitable carrier materials are organic materials such as plastics or cellulose. It is also preferable for a carrier-material element to have its own capillarity. An example is a cellulose fibre, such as a wood fibre, which inherently forms a considerably finer capillary space than the capillarity formed between two fibres. It is also important for the latent heat storage material itself to form homogeneously distributed hollow structures. These structures are of particular importance for the performance or response of the latent heat body. Firstly, such hollow structures provide yielding spaces as the volume changes during heating or cooling. This volume change may generally be of the order of 10% of the volume. As carrier-material elements, there may furthermore be used fibres of very different lengths and diameters. Suitable elements are in particular also ceramic fibres, mineral wool, plastics fibres and other suitable fibres, such as for example cotton or wool. Ceramic fibres used preferably substantially comprise Al2O3, Si2, ZrO2 and organic additions, and the quantities in which the components are present may vary considerably. Depending on the proportions selected, the density of the ceramic fibres fluctuates, preferably within a range from 150 to 400 kg/m3. With regard to the mineral wool, preference is given to using rock wool with or without the addition of thermosetting synthetic resins, and the wool may furthermore contain glass fibres. The density fluctuates as a function of the composition selected for the individual case and preferably lies in a range between 200 and 300 g/m3. Plastic fibres which are suitable as carrier-aterial elements preferably contain base materials such as polyester, polyamide, polyurethane, polyacrylonitrile or polyolefins. In this regard, it is particularly preferable for the latent heat storage material to be a paraffin as described in DE-A-43 07 065. The entire contents of this prior publication are hereby incorporated into the disclosure of this application, also for the purpose of including features of this prior publication in claims of the present application.
In the solidified state, such a paraffin has crystal structures which are modified by a structural additive, preferably so as to create hollow structures, such as for example hollow cones. This makes it possible to significantly improve the response of the latent heat storage material when heat is introduced. As a result, the latent heat storage material, such as paraffin, adopts, as it were, a porous structure. When heat is introduced, constituents of the latent heat storage material which melt more easily can flow through the hollow structures provided in the material itself. A type of micro-convection is able to establish itself, if appropriate also with regard to air inclusions which are present. The result is a highly efficient mixing together. There is a further advantage with regard to the abovementioned expansion behaviour in the event of a phase change. The structural additive is preferably dissolved homogeneously in the latent heat storage material. In detail, structural additives such as those based on polyalkyl methacrylates (PA-MA) and polyalkyl acrylates (PAA) have proven suitable as individual components or in combination. Their crystal-modifying effect is brought about by the fact that the polymer molecules are incorporated into the growing paraffin crystals and prevent this crystal shape from growing further. Because of the presence of the polymer molecules even in associated form in the homogeneous solution in paraffin, paraffins may grow on the special supranuclear assemblies. Hollow cones which are no longer able to form networks are formed. Due to the synergistic action of this structural additive on the crystallization behaviour of the paraffins, cavities are formed and therefore the ease with which the heat storage medium paraffin can flow through (for example for air or water vapour which is included in the latent heat storage body or for liquefied phases of the latent heat storage material, i.e. of the paraffin itself) is improved compared to paraffins which have not been compounded in this way. In general, suitable structural additives also include ethylene/vinylacetate copolymers (EVA), ethylene/propylene copolymers (OCP), diene/styrene copolymers, both as individual components and in a mixture, as well as alkylated naphthalenes (Paraflow). The level in which the structural additives are present starts at a fraction of a per cent by weight, realistically at about 0.01 per cent by weight, and reveals significant changes, in terms of an improvement, in particular up to a level of about one per cent by weight.
In more detail, it is also preferable for an additive which leads to a thick liquid to be added to the latent heat storage material. A conventional thixotropic agent can be used for this. Even in the heated state, in which the latent heat storage material is usually liquefied, the consistency is then still that of a heavy liquid, in the sense of a gelatin-like consistency. Even in the event of such a latent heat storage body being cut into unintentionally, there is no leakage, or only insignificant leakage, of latent heat storage material.
Preferably, a latent heat body formed in this way is also completely surrounded with a cover, preferably a plastics film. The completely surrounding cover prevents any softened or liquefied latent heat storage material from leaking. The surrounding cover may also comprise urea. The sheet may be immersed in a molten covering material, i.e. for example urea or a plastic, such as for example nylon (polyamide). With urea, there is the advantage of a considerable flame-retardant action. It is particularly important to prevent leakage in the event of the rated operating parameters being exceeded. This applies in particular if the rated parameters are exceeded.
Preferably, the carrier structure comprises a fibrous body which is composed of individual fibres. In this case, commercially available fibreboards may be used, although relatively soft fibreboards are in this case preferred. Hard fibreboards are only able to accommodate the latent heat storage material to a limited extent. The fibres preferably have an inherent capillary action. When such a fibreboard is being impregnated with a paraffin-based latent heat storage material, the fibres fill up with paraffin by sucking it in and are xe2x80x9cgrownxe2x80x9d. In addition, the capillary spaces between the fibres are also filled with the latent heat storage material. A further configuration provides for the carrier material to be a nonwoven, for example a conventional absorbent nonwoven such as those which are commercially available for example for sucking up oil, acids or other liquids. In particular, it may be a nonwoven which consists entirely of polypropylene fibres. In this case, the fibres may also be joined together, for example by welding, in the sense of the general teaching mentioned above. However, the support structure provided by the nonwoven is also of independent importance. It is particularly advantageous that the abovementioned fibre mat, and also the nonwoven, are strengthened when impregnated with the paraffin-based latent heat storage material. The structure becomes more rigid. By way of example, a fibreboard of this nature acquires a higher compressive strength and is stronger when walked on, for example. In addition, the sound properties of latent heat bodies created in this way are also improved. There is a higher insulation against structure-borne sound. The footfall sound, for example when a latent heat body of this nature is used in the floor area, is effectively damped. In a further advantageous configuration, such carrier structures which can be impregnated with from two to ten times their own weight of latent heat storage material are used. By way of example, the abovementioned fibreboards are impregnated with from three to four times their own weight of latent heat storage material. However, the impregnation is not carried out to such an extent that over-swelling effects arise. It is also recommended to close off the capillaries on the outside, for example by grinding. This closure reinforces the effect of the surrounding cover mentioned above. In this case, it is advantageous for the capillaries to be closed off before the carrier material is impregnated with the latent heat storage material.
Further particular teaching of the invention relates to a configuration of the paraffin-based latent heat storage material which is such that there is still flexibility even in the strengthened state. Thus, in combination with the carrier-material elements, it is possible to achieve a flexible element, such as for example a seat cushion or a bandage. To this end, there is provision for the (paraffin-based) latent heat storage material to contain a proportion of mineral oil and/or of polymers, rubbers and/or elastomers. The rubbers and/or elastomers in particular lead to a higher flexibility. These are present in a proportion of less than 5%. If the polymers are not elastomers, they do not increase the flexibility and simply provide (possibly additional) protection against leakage the polymers amount to no more than 5% by mass of the latent heat storage material. Preference is given to a highly refined mineral oil, for example a mineral oil which is customarily referred to as white oil. The polymers are crosslinked polymers which are produced by copolymerization. Together with the mineral oil, by constituting a three-dimensional network or by their physical crosslinking (nodular structure), the crosslinked polymers form a gel-like structure. These gels exhibit a high level of flexibility combined with stability with respect to the action of mechanical forces. The paraffin is enclosed in this structure in the liquid state. When the phase changes, at crystallization, the paraffin crystals which are formed are surrounded by the gel structure, resulting in a mixture which overall is flexible.
In a possible application, a latent heat storage material which contains paraffin with a melting temperature of 50xc2x0 C. and a copolymer with a melting temperature of 120xc2x0 C., can be heated to a temperature of 125xc2x0 C., so that initially the two components are mixed together uniformly, and the low-viscosity mixture can be absorbed by the carrier material, owing to the capillary forces which are active therein, until the carrier material is completely saturated. During subsequent cooling, the paraffin crystals which form are surrounded by the copolymer. At for example a possible upper operating temperature of the latent heat body of 80xc2x0 C., only the paraffin component, but not the copolymer, is liquefied. This results in the advantageous effect that the paraffin cannot emerge from the copolymer, but rather remains in the carrier material with the copolymer. It is pertinent to the invention that the desired paraffin-retention capacity in the latent heat body when the carrier material described above is used can be achieved even where the copolymer forms less than 5% by mass of the latent heat storage material. The desired paraffin-retention capacity can be achieved even when the copolymer forms significantly less than 5% by mass in particular by means of an interaction carried out in a controlled manner of capillary forces in the holding spaces of the carrier material and/or of crystal structures of the paraffins which are influenced by means of structural additives and/or of the thixotropic agents which thicken the latent heat storage material and/or by means of the above-described closure of the capillaries and, if appropriate, a surrounding cover of the latent heat body. One advantage of the invention in this case is that as the content by mass of copolymers decreases, the content by mass of paraffins in the total mass of the latent heat storage material increases, and in this way it is possible to achieve a higher heat-absorption capacity while the total mass remains unaltered.
Together with the carrier material which is described in more detail above, a further result is a desired structural strength in the context of flexibility. However, other carrier materials than those mentioned above may also be employed. Examples include open-cell foams. With regard to the polymers, possible examples are styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS) or styrene-ethylene/butylene-styrene (S-EB-S). In the case of the styrene-ethylene/butylene block copolymer, use is made of an agent which is known under the trade name xe2x80x9cKRATON Gxe2x80x9d, marketed by Shell Chemicals. However, other known Kraton modifications may also be employed. This block copolymer is preferably suitable as a thickening agent for increasing the viscosity or as an agent for increasing the elasticity. The thickening agent may be a delayed action agent. Kraton G is a thermoplastic, and there are a number of types of copolymers in the Kraton G series which are of different structures. It is possible to differentiate in particular between the block and triblock copolymers, the molecular weight of which varies and which exhibit different ratios of styrene content to elastomer content. Of the known Kraton G types, the types known as G 1650, G 1651 and G 1654 may preferably be used.
Furthermore, it is also possible to use copolymers, such as for example HDPE (high-density polyethylene), pp (polypropylene) or HDPP (high-density polypropylene).
A further subject of the application is a paraffin-based latent heat storage material which contains an additive in one of the forms described above. Both the latent heat body and the latent heat storage material may furthermore and in combination contain an additive which forms the hollow structures mentioned above.
The paraffin-based latent heat storage material according to the invention may furthermore also be used without a carrier material, i.e. without a supporting matrix. For reasons of melting/storage capacity and for functional reasons, the copolymer content is always less than 5%. The gel formed is held in container sleeves, such as for example film/foil bags.
The pertinent factor is for the abovementioned additive of mineral oils and polymers on the one hand to be homogeneously distributed in the paraffin or for the paraffin to penetrate homogeneously through this additive and, on the other hand, for there to be no chemical interaction between the additive and the paraffin. Furthermore, it is particularly important for the selection to be made in such a way that there are virtually no differences in density between the additive and the paraffin, so that it is impossible for such density differences to cause any physical separation.
As has already been explained in the introduction, it is possible, in combination with one or more of the features explained above, for the latent heat body according to the invention to contain a number of latent heat part-bodies. In the context of the invention, a latent heat part-body is a cohesive, separate part or constituent of a latent heat body according to the invention which is inherently able to combine all the physical, chemical and structural features of the latent heat body or any desired selection of these features. Preferably, a latent heat part-body contains a carrier-material part and the latent heat storage material which is accommodated in capillary-like holding spaces in this carrier-material part. The abovementioned carrier-material part may have any desired combinations of the features of a carrier material which have been explained so far. In a preferred embodiment, the latent heat body contains a relatively large number, which is partly determined by its size and shape, of latent heat part-bodies, which can be arranged next to one another in regular and/or irregular form. In this way, it is possible to produce latent heat bodies of virtually any desired shape at low cost, since the latent heat part-bodies can be produced in large numbers on an industrial scale irrespective of the shape of the desired latent heat bodies. In a preferred configuration of a latent heat body formed from a plurality of latent heat part-bodies, the carrier-material parts which are included in the latent heat part-bodies also adjoin one another. These carrier-material parts are to be clearly distinguished from the carrier-material elements from which the carrier material, as explained above, is assembled, for example by adhesive bonding. Within individual carrier-material parts, the carrier-material elements form cohesive structures which include capillary-like holding spaces. However, adjacent latent heat part-bodies may also be held cohesively together if, for example, the arrangement is such that carrier-material elements of mutually adjoining carrier-material parts hook together in the respectively adjacent cohesive structures. Latent heat part-bodies may be held more cohesively together by connecting the latent heat storage material by means of adjacent latent heat part-bodies.
Preferably, the volumetric ratio of latent heat body to latent heat part-bodies has a value of at least 10, although lower or significantly higher volumetric ratios may also be appropriate. Moreover, an individual latent heat body may also contain latent heat part-bodies of different sizes and/or shapes. Furthermore, it is also possible for individual latent heat part-bodies to be of elongate shape and to be formed as strips, at least in the broadest possible sense. Alternatively, a latent heat part-body may also be in the form of a flake. Furthermore, the latent heat part-bodies may also be formed in the shape of spheres, ellipsoids, cubes, cuboids, pyramids, cylinders and the like. The selection of the number, sizes and shapes of the latent heat part-bodies of a latent heat body may in this case be oriented according to the size and shape of the desired latent heat body and to the particular requirements in terms of strength or deformability. In a further preferred embodiment of the latent heat part-body, the latter has a surrounding cover which comprises, for example, a film/foil material, in particular an aluminium foil or a polypropylene film. A film/foil offers the advantage of ease of deformability, so that adjacent latent heat part-bodies can nestle against one another, and it is substantially possible to avoid cavities between the latent heat part-bodies. As an alternative, or in combination with this measure, it is possible for a number of adjacent latent heat part-bodies also to be provided with a common outer surrounding cover, which may likewise be one of the films/foils mentioned above. Furthermore, it is possible for the common outer surrounding cover to have a comparatively rigid wall, i.e. a wall which is more difficult to deform than the latent heat body or the latent heat part-bodies. If a rigid wall of this nature is formed as a hollow body, its interior space can be virtually completely filled with latent heat part-bodies of size, shape and number which are appropriate to the particular requirements, even if the common outer surrounding cover is of complicated geometric shape. In this case, a pressure may be applied to the latent heat part-bodies, in order to prevent relatively large cavities from forming in the rigid common surrounding cover, so that these part-bodies are compacted at least in certain areas. In the case of latent heat part-bodies of a latent heat body which have been compacted in this way, the cavities between latent heat part-bodies may, for example, form less than 1% by volume of the total volume of the latent heat body. The surrounding cover of the individual latent heat part-bodies and/or the common surrounding cover of the latent heat part-bodies of a latent heat body are in this case preferably configured in such a way that they are impermeable to latent heat storage material.
In an alternative advantageous configuration of a latent heat body, the latter contains a plurality of latent heat part-bodies which are surrounded by a common sleeve which is permeable to a heat transfer medium and which are preferably spaced apart from each other within this sleeve. By virtue of the spacing between the latent heat part-bodies, cavities are formed between the part-bodies, which cavities represent suitable flow paths for the heat-transfer medium. In particular, there is provision for a heat-transfer medium to pass out of an outer surrounding region, through the outer surrounding cover, which is permeable to this medium, of the latent heat body, into the interior of this body, where it flows through the cavities formed between the latent heat part-bodies and then leaves the latent heat body again through its common surrounding cover, which is permeable to this medium. A latent heat body which has heat-transfer medium flowing through its interior in this way is distinguished by a particularly rapid heat transfer from or to a heat-transfer medium. The common surrounding cover of the latent heat part-bodies may, for example, be in the form of a network or lattice, i.e. both readily deformable and rigid structures are possible. The entry and outlet openings in the common outer surrounding cover of the latent heat part-bodies contained in the latent heat body are suitably dimensioned in such a way that the heat-transfer medium can enter and leave the latent heat body substantially without obstruction and that moreover it is impossible for any latent heat part-bodies to pass through these openings. The volumetric ratio between the latent heat part-bodies contained in the surrounding cover and the cavities located between these part-bodies may lie within a wide range and, in numerical terms, may be considerably higher or lower than one. If a liquid is used as heat-transfer medium, the density of the latent heat part-bodies may be set in such a way that they are held suspended in the heat-transfer medium. In this way, the cavities formed are maintained, but it is possible to further accelerate the heat exchange with the latent heat part-bodies by causing them to circulate in flow terms. Examples of suitable liquid heat-transfer media are water or oils and, in addition, other suitable liquids. Even if a gaseous heat-transfer medium, e.g. air, is used, it is possible to counteract settling of the latent heat part-bodies which are contained in the common surrounding cover by effecting a controlled flow which leads to the latent heat part-bodies floating or circulating continuously. This can be enhanced by a particular configuration of the latent heat part-bodies, in which a surface area which is in each case large in relation to the weight of a particular latent heat part-body is effected. Consideration may be given, for example, to providing the latent heat part-bodies in the form of flakes. Furthermore, the latent heat part-bodies may have one or more of the features mentioned above.
As has already been stated, a latent heat body formed as above can be installed as a floor panel in a floor heating system.
However, the invention also relates to further applications of such latent heat bodies.
A first application comprises a plate heat exchanger which has such latent heat bodies as its plates. In this case, medium can be applied to the plate elements on both sides. By way of example, regenerative heat exchangers, such as those which are known in thermal power stations, may also be equipped with such heat exchangers. Specifically, such a plate element may also be of helical shape. To form and maintain the helical configuration, spacer elements are disposed between the layers, although this also applies to plate elements with planar surfaces. These spacer elements are arranged in the form of a grid, in such a manner that flow paths are left open.
In a further embodiment, it is preferred for such a plate element to be formed as a cladding panel in the construction sector. In this case, it is particularly advantageous if the cladding panel is disposed at a distance from the wall of a house. The chimney effect which is then established between the house wall and the cladding panel, which in this case is formed as a latent heat storage element, can thus bring about a cooling effect, partially by storing heat in the latent heat body. Furthermore, the thermal behaviour over the course of time is also improved. For example, after the sun has set, the latent heat body still continues to emit heat, including radiant heat, at constant temperature to the wall of the house over a prolonged period. At the same time, such a latent heat body constitutes a panel which provides a relatively high heat insulation. The insensitivity of such a cladding panel to the effects of weathering is also advantageous. The impregnation with paraffin also provides a hydrophobic property.
In further detail, a capillary-breaking grid structure, for example made from a plastics, may also be arranged in such a latent heat body, in addition to the carrier structure described above, for all the applications which have been described in the preceding text. In this way, the necessary equilibrium between capillary forces and gravity, when the latent heat body is arranged in a vertical position, can be achieved at any time in the filled fibrous structure. To allow the diffusion of water vapour, suitable overflow openings, such as slots, holes and the like, are located in the latent heat bodies. It is particularly important here for the thermal conductivity of this grid structure to approximately correspond to that of the latent heat storage material. Conventional metal structures are therefore to be rejected, since the thermal conductivity is too high.
With regard to the embodiment of a floor heating system comprising latent heat bodies of this nature, it is also proposed for latent heat bodies containing different latent heat storage materials in terms of the melting temperature or the phase-transition temperature to be arranged above one another. In this case, the latent heat body on which a heater element, such as for example a resistance-heating wire, acts directly is suitably equipped with latent heat storage material of the highest phase transition temperature, while the latent heat storage body with the phase-transition temperature which is lowest in relative terms is arranged close to the surface of the floor. Such a floor heating system can advantageously be provided as a night storage heating system, since the time offset can be used to good effect without, as with other known night storage heating systems, having to accept excessive temperatures.
The invention furthermore relates to a process for producing a latent heat body with paraffin-based latent heat storage material accommodated in a carrier material which has holding spaces. According to the invention, it is specified that the latent heat storage material is liquefied, and that the latent heat storage material which has previously been liquefied is fed to capillary-like holding spaces in the carrier material which suck the liquefied material in automatically. Liquefaction of the latent heat storage material may in this case preferably be achieved by heating. The liquefaction aims to make the latent heat storage material able to flow readily, i.e. essentially at achieving a low viscosity and a homogeneous state without the inclusion of relatively large pieces of solid material. The low viscosity provides an essential condition for the latent heat storage material to penetrate into the holding spaces, under the automatic sucking action of the capillary-like holding spaces in the carrier material, when it is fed to these spaces. To this end, the carrier material may, for example, be impregnated with liquefied latent heat storage material. The liquefied latent heat storage material may, for example, be fed to automatically sucking capillary-like holding spaces in the carrier material by immersing the carrier material in liquefied latent heat storage material. Before and/or during this immersion, process parameters which influence the automatic uptake of the latent heat storage material in the carrier material can be influenced so as to promote this uptake. By way of example, thermal energy may be continuously supplied to the latent heat storage material in order to promote the liquefaction. Furthermore, pressure may be applied to the liquefied latent heat storage material, thus likewise promoting the automatic uptake of the latent heat storage material in the capillary-like holding spaces in the carrier material.
The automatic sucking action of the holding spaces of the carrier material for liquids is based on the capillary-like form of the holding spaces which has already been mentioned above. The automatic sucking action of the capillary-like holding spaces for liquefied latent heat storage material and its attempt to retain this material are intensified as the size of diameter of the capillaries or of the inner radii of capillaries is selected to be smaller and as the surface tension of the latent heat storage material with respect to air is selected or set to be higher, and as the extent to which the carrier material selected can be wetted by latent heat storage material increases. In the process according to the invention for producing a latent heat body, on the basis of these relationships for setting a desired, in particular a maximum possible automatic sucking action of the holding spaces with regard to the latent heat storage material, it is possible to proceed in such a way that a carrier material with a surface tension which is as high as possible is selected and in such a way that the individual carrier-material elements have inner capillaries with preferably low radii of curvature and/or external shapes with narrow radii of curvature, in particular also have sharp edges or corners. Preferably, the carrier material is assembled from individual carrier-material elements, for example by adhesive bonding, and capillary-like holding spaces are formed at least between the carrier-material elements. When assembling the carrier-material elements it is therefore also possible to influence the automatic sucking action, in that preferably narrow, in particular crack-like capillaries are formed in order to increase this action. Furthermore, the process according to the invention may be employed to produce a latent heat body based on carrier material and latent heat storage material having all the features described above or having combinations of selected features.
In a suitable variant of the process according to the invention, the carrier material which has been impregnated with latent heat storage material is divided into a number of latent heat part-bodies, in which case the division may be carried out by means of sawing and/or cutting and/or tearing or also according to further known separating methods. For example, it is possible to impregnate a fibreboard made from cellulose fibres, which has been selected as the carrier material, with paraffin-based latent heat storage material which has previously been liquefied and to saw the impregnated carrier material into elongate, in particular strip-like latent heat part-bodies. As a further variant, a fibrous nonwoven, for example, which has been selected as the carrier material, after impregnation with latent heat storage material, could be torn into a desired number of comparatively small latent heat part-bodies, in which case the latter may be of flake-like form or of some other form. In one refinement of the production process according to the invention, the latent heat body and/or the latent heat part-bodies may be compressed, in order in this way to be compacted or given a preferred shape. It is also possible for the latent heat body and/or the latent heat part-bodies to be provided with a surrounding cover which may comprise a film/foil, in particular an aluminium foil or a polypropylene film. In this case, it is preferable for the latent heat body or the latent heat part-bodies to be completely surrounded by a surrounding cover which is impermeable to latent heat storage material and to be sealed in this cover, for example by welding, in such a manner that it is impossible for any latent heat storage material to leak out of the surrounding cover. In a refinement of the process according to the invention, the latent heat part-bodies of the latent heat body may also be provided with a surrounding cover which surrounds them together and may likewise have the properties mentioned above. In particular, it is possible to provide a readily deformable common surrounding cover which, in combination with a multiplicity of relatively small latent heat part-bodies contained therein, leads to a desired deformability of the latent heat body. As an alternative, it is possible to use a common surrounding cover which has a higher rigidity or lower deformability than impregnated carrier material. A surrounding cover of this nature, which may be any of a large number of types of casing used in everyday items, may, according to a variant of the process according to the invention, be filled with any desired number of latent heat part-bodies, and then, in a further working step, the latent heat part-bodies can be sealed in the common surrounding cover. It is thus possible, using the process according to the invention, to virtually completely fill any desired cavities in everyday items with impregnated carrier material in a simple, time-saving and inexpensive manner.
In an advantageous refinement of a latent heat body according to the invention, there is provision, in conjunction with one or more of the features which have been explained thus far, for at least one microwave-active substance to be present in the latent heat body. A microwave-active substance in the context of the invention is to be understood as meaning a substance which is internally heated under the influence of radiation from so-called microwaves owing to its molecules being excited to move by the high-energy electromagnetic radiation. Microwaves are adjacent to the wavelength range of infrared radiation, at higher wavelengths. In this respect, a minimum wavelength of approximately 1.4xc3x9710xe2x88x923 m is to be assumed, and the internal heating can be optimized within the wavelength range which is of technical interest by adapting the wavelength selected to the molecular structure of the microwave-active substance which is to be used. A latent heat body which contains a microwave-active substance of this nature consequently has the advantage that considerably shorter times are required to supply a certain amount of energy compared to heat transfer through shorter-wave radiation, thus allowing correspondingly quicker heating. In particular, consideration is given to distributing the microwave-active substance uniformly in the latent heat body, so that a corresponding uniform heating is to be observed. In the context of the invention, uniform distribution does not necessarily have to mean an homogeneous distribution, since uniform heating of the latent heat body as a result of thermal conduction processes which is adequate for technical applications may also be achieved when the microwave-active substance is distributed along the latent heat body in accumulated patches which are sufficiently close together. In this connection it is possible, for example, for carrier-material elements to contain the microwave-active substance, for the microwave-active substance to be contained in capillary-like holding spaces between the carrier-material elements, which for example have been assembled to form a carrier material by adhesive bonding, or in capillary-like holding spaces inside the carrier elements, or for the microwave-active substance to be contained in cavities which are formed between a plurality of latent heat part-bodies; combinations of these proposed distributions are also conceivable. A uniform distribution of the microwave-active substance in the latent heat body is promoted by the microwave-active substance being contained in it in powder and/or granule and/or fibre form. If the microwave-active substance is to be held in the latent-heat-body cavities which are formed between latent heat part-bodies, finally relatively large cohesive structures of the microwave-active substance may also be advantageous, with dimensions which may be of comparable size to those of the latent heat body. Consideration may be given in particular to an interwoven mesh or network of a microwave-active substance which is integrated into the latent heat body. As an alternative, or in combination with above-described forms of distribution of the microwave-active substance as a solid body, it may be expedient for the microwave-active substance to be a liquid at least at the temperature at which the latent heat body is used, in which case, in this context, all flowing media are to be included in this definition. In terms of selecting the microwave-active substance, in principle all substances which experience internal heating under the action of microwaves are to be considered for the purposes of the invention. It is preferably a substance which is included in one of the materials groups consisting of glass materials, plastics materials, minerals, metals, in particular aluminium, coal and ceramics. It is also possible for a plurality of different microwave-active substances to be combined with one another in a latent heat body. This allows more rapid heat transfer to the latent heat body at a plurality of wavelengths or within a definable wavelength range. Preferred embodiments of the microwave-active substance which may be mentioned by way of example are granular glass bodies, granular plastics, mineral fibres, ceramic fibres, coal dust, metal, in particular aluminium powder, and a filament/wire, which is likewise preferably formed from metal and may be processed further to form an interwoven mesh.
To produce a latent heat body which can be heated by microwaves, a microwave-active substance has to be added to the latent heat body or a constituent of this body in a process step which preferably aims to achieve a uniform distribution of the microwave-active substance in the latent heat body. The procedure may be such that the microwave-active substance is added to the carrier-material elements while they are being produced. In particular, the carrier-material elements may also themselves be produced directly from microwave-active substance. As an alternative, or in combination with this measure, it is possible to incorporate the microwave-active substance continuously or discontinuously in the capillary-like holding spaces which are formed when the carrier material is being assembled from carrier-material elements, for example by adhesive bonding, while this assembly is taking place. This may, for example, be achieved by the fact that, with a layered structure of the carrier material, after a respective layer has been completed by adhesive bonding of carrier-material elements, a microwave-active substance which is in dust or powder form is dusted onto the surface of the layer and, after excess dust or powder has been removed, a further layer of carrier-material elements is placed on top, these process steps being repeated as many times as desired. In a latent heat body which contains a plurality of latent heat part-bodies, the microwave-active substance may furthermore also be incorporated in the cavities which are formed between latent heat part-bodies. The microwave-active substance may in this case be processed both as a powder and as granules or fibres and, furthermore, also as a larger structure, in particular as a filament/wire or an interwoven mesh. In this case, the procedure is preferably such that, firstly, a layer of latent heat part-bodies is arranged, for example, in a common surrounding cover, and then the microwave-active substance is deposited on this layer and in the spaces between these part-bodies, and then a further layer of latent heat part-bodies is applied; it is possible to repeat these working steps as many times as desired. In a further variant to the production process according to the invention, the microwave-active substance is added to the latent heat storage material before the latent heat storage material is fed to the capillary-like holding spaces in the carrier material. In this case, it should preferably be ensured that the microwave-active substance is distributed uniformly in the latent heat storage material, so that the microwave-active substance is also sucked into the capillary-like holding spaces in the carrier material in a uniform distribution, where it is present in a uniform distribution with the paraffin-based latent heat storage material. As an alternative, or in combination with the processing of the microwave-active substance in the solid state described above, it is also possible for the microwave-active substance to be added to the latent heat body in liquid form; in this case, in principle all the addition techniques described above are to be considered.
If the microwave-active substance in its crude state cannot be used directly in the production of a latent heat body, the process according to the invention for producing a latent heat body which is to be heated by microwaves comprises additional process steps in which a desired state of the microwave-active substance can be achieved. These steps include, for example, working the microwave-active substance into a powder, granules or fibres, preferably by mechanical processes such as for example sawing, cutting, milling and tearing. If it is intended to use the microwave-active substance in filament/wire form or as an interwoven mesh, the process according to the invention for producing a latent heat body which can be heated by microwaves also encompasses process steps in order to process the microwave-active substance into structures which are appropriate for the particular requirements. In particular, these steps include the wire-drawing of suitable materials and further processing of the wires obtained to form an interwoven mesh.